61 

 GEOLOLGICAL FEATURES OF THE DISTRICT. 



Mr. Pdeton then said : I have been requested to point out to you the 

 principal geological features of the landscape now before us, but I fear I shall 

 be but a blind guide, as I was never here before ; and there is so much mist 

 that many of the most prominent objects are very obscurely visible. "We are 

 placed in the centre of a typical district ; for in the immediate neighbourhood 

 of the hill on which we stand "we may find rocks representing almost every 

 member of the Silurian system. An ideal section of the district would show an 

 anticlinal asis of those Cambrian rocks which, until recently, were supposed 

 to be the oldest sedimentary rocks in Great Britain. Thrown off on either side 

 by this axis, we have resting, one upon another, in ascending order — First, the 

 Lingula flags ; next the LlandeUo formation ; then the Llandovery and Caradoc 

 rocks— are overlaid in their turn by the Werdock and Ludlow group ; then the 

 8,000 or 10,000 feet of Old Red Sandstone, the uppermost beds of which are 

 overlaid by the varied strata of the Carboniferous system. In the great ridge of 

 the Lungmynd which you see opposite, towering through the mist, you have the 

 axis I have spoken of, composed of those green and purple slates — those ancient 

 grits and conglomerates which Sir Roderick Murchison was the first to prove 

 identical with the Cambrian strata, though formerly supposed to underlie them. 

 Against these Longmynd or bottom rocks, which are much upheaved and con- 

 torted, rest on the N.W. the Lingula Flags, consisting of black shales with 

 Lingula; and a few Trilobites overlaid by those quartoze rocks which form the 

 peculiar castle-like masses which you see rising up here and there along the crest 

 of the Stiper-stones. The Stiiier-stones ridge, in fact, represents, in this neigh- 

 bourhood, the Lingula Flags series. On the N.W. slope of this ridge we find 

 the Llandeilo rocks, which occupy the whole of the mining district of Shelve, 

 and are curiously interstratified with their bands of Volcanic rocks of the 

 Felspathic group, probably the restUt of successive irruptions of sabmarine 

 volcanos. The Corndon hill, which rises so boldly a few miles to the N. of 

 Bishop's Castle, occupies the centre of this district, and is composed chiefly of 

 greenstone. You see it yonder amid the mists, the highest point to the north. 

 The country to the N.W., including the spot on which we stand, is occupied by 

 the Wenlock and Ludlow series — the characteristic limestones of which are, 

 however, wanting. The Llandovery rocks are represented by a small patch to 

 the N. of Bishop's Castle, and another at Linley and Norbury. The Caradoc 

 series is nowhere visible on the surface. On the other hand we shall find the 

 ■whole of the Lingula Flags and Llandeilo rocks absent on the S. E. of the Long- 

 mynd ridge having been faulted down : while the Llandovery rest immediately 

 upon the Cambrian along the base of the hill on the south and east. The Caradoc 

 sandstone overlies these, and occupies the district in the centre of which rise the 

 igneous masses of Magleth and Hope Bowdler Hills, the Caradoc, and Lawley. 

 These all stand upon the line of upheaval, which is marked by one of the 

 longest lines of fault in the kingdom, running from S.W. to N.E.,— from far 



